The invention relates to an electrochemical energy storage system. The invention furthermore relates to a battery.
A lithium-sulphur battery is known from DE 10 2010 018 731 A1, comprising a first electrode comprising lithium, a second electrode comprising sulphur and/or a lithium sulphide, a separator between the electrodes and an electrolyte in the separator. Here, the separator comprises a non-woven fleece made from polymer fibers.
An electrode for a battery is furthermore known from US 2011/0281156 A1, which is provided with carbon nanotubes, wherein the carbon nanotubes have a silicon matrix, by means of which volumetric changes to the battery are able to be compensated for during electrochemical processes within the battery.
The object of the invention is to specify an improved electrochemical energy storage system compared to the prior art, as well as an improved battery.
An electrochemical energy storage system comprises at least two electrodes, between which a separator is arranged. Provision is made according to the invention for the separator to be designed to be mechanically flexible.
The electrodes are formed as an anode and a cathode, wherein the separator divides the electrodes from one another spatially and electrically. Here, the separator is necessarily designed to be ion-permeable, such that the active material of the anode, e.g., lithium ions, is able to diffuse towards the cathode during a discharge process of the electrochemical energy storage system and back to the anode during the charging process. These electrochemical processes lead to volumetric changes to the electrodes, which is also referred as electrode “breathing”. The mechanically flexible design of the separator enables the volumetric changes to the electrodes to be compensated for, such that the separator is able to be configured with correspondingly smaller dimensions compared to the prior art, since no additional construction space has to be present to compensate for the volumetric changes for the arrangement of the electrochemical energy storage system. In addition, an equally high degree of compression on single cells within the electrochemical energy storage system can take place.
The mechanically flexible design of the separator enables a passive positional change to the separator between the electrodes, depending on the electrochemical processes taking place between the at least two electrodes. The separator is then, for example upon enlargement of a cathode volume, shifted in the direction of the anode, whose volume is thus reduced.
The separator is alternatively or additionally designed to be elastic, wherein it may change its shape and/or its volume depending on the electrochemical processes taking place between the electrodes. The shape and/or volume change of the separator here takes place in a substantially passive manner depending on the volumetric changes to the electrodes, wherein a position of the separator is able to be altered or remains fixed. This means, for example, that if the volume of the cathode increases as a result of a discharge of the electrochemical storage system, the separator is deformed accordingly in the direction of the anode with its side facing the cathode. The cathode can therefore expand within the electrochemical energy storage system without external deformations of the single cells or the electrochemical energy storage system arising. Here, the separator can be deformed in the direction of the anode with only a very small loss of volume, wherein the side of the separator in the anode region facing the anode spreads out, for example with a bulge, or the volume of the separator is compressed on the cathode side in such a way that no or only very little bulge-like spreading out of the separator takes place on the anode side. Here, however, care must be taken to ensure that an ion exchange between the electrodes is secured.
According to a preferred exemplary embodiment, the separator is formed from a glass fiber membrane. The glass fiber membrane has a corresponding porosity, into which, according to a further preferred exemplary embodiment, a liquid, organic electrolyte is able to be poured, by means of which the active material of the anode is able to be transported through the separator. Alternatively, the separator may also be formed from a porous ceramic film or a porous polymer membrane.
The electrodes of the electrochemical energy storage system are each formed from a substrate and are coated with a composite material comprising an electrically conductive matrix and an active material which is integrated into the electrically conductive matrix in a defined manner.
The electrically conductive matrix is, for example, formed from a porous and mechanically flexible carbon structure such as, for example, graphite or carbon black. The mechanical flexibility of the carbon structure enables the aforementioned volumetric changes to the electrodes, in particular the active material, in a manner that is as free from damage as possible and without incurring any loss of the electrical contacting of the electrodes. The compensation for the volumetric changes to the active material in the electrodes can therefore be further improved.
The electrically conductive matrix of at least one of the electrodes, in particular the anode, additionally or alternatively comprises a silicon structure. Compared to the carbon structure, silicon has a reduced degree of electrical conductivity, but has the property of intercalating a larger amount of active material, in particular of metal ions such as lithium ions, and is therefore particularly suitable for coating the anode.
The silicon structure particularly preferably comprises nanoscale, tubular structures, such that the mechanical flexibility of the electrically conductive matrix can be increased in combination with the mechanically flexible carbon structure. As a result, the performance and lifespan of the electrochemical storage system can be improved considerably with respect to the prior art.
The invention moreover relates to a battery comprising at least one electrochemical energy storage system, by means of which the performance and lifespan of the battery can be increased compared to the prior art.
Exemplary embodiments of the invention are illustrated in greater detail below by means of drawings.